1. Field of the Invention
The present invention relates to a raster display system and, more particularly, to a circuit and method that allows the amplitudes of vertical correction signal components to be adjusted independently.
2. Related Art
Raster display system are used in a variety of application such as televisions and computer displays. FIG. 1A shows a cross-sectional side view of a conventional raster display system 100. Raster display system 100 includes an electron gun 110, a deflection system 120, and a screen 130. Electron gun 110 generates and accelerates an electron beam 115 toward deflection system 120. Deflection system 120 deflects electron beam 115 horizontally and/or vertically at screen 130. Screen 130 includes a phosphor-coated faceplate that glows or phosphoresces when struck by electron beam 115.
Deflection system 120 includes a horizontal deflection generator 122, a horizontal deflection coil 124, a vertical deflection generator 126, and a vertical deflection coil 128. Horizontal deflection coil 124 and vertical deflection coil 128 are collectively referred to as the yoke. Although not shown, horizontal deflection coil 124 and vertical deflection coil 128 are wound a ninety-degree angle relative to one another. Horizontal deflection generator 122 generates a horizontal deflection current signal IH. When horizontal deflection current signal IH passes through horizontal deflection coil 124, a magnetic field is created that deflects electron beam 115 horizontally. The horizontal angle of deflection (not shown) is proportional to the direction and the magnitude of horizontal deflection current signal IH. Similarly, vertical deflection generator 126 generates a vertical deflection current signal IV. When vertical deflection current signal IV passes through vertical deflection coil 128, a magnetic field is created that deflects electron beam 115 vertically. The vertical angle of deflection xcex8 is proportional to the direction and the magnitude of vertical deflection current signal IV.
FIG. 1B is a front view of raster display system 100. Deflection system 120 deflects electron beam 115 from a first side of screen 130 to a second side of screen 130 to draw a first line L1. Electron beam 115 is then briefly turned off, moved downward, and brought back to the first side of screen 130 by deflection system 120. Electron beam 115 is then turned on and deflection system 120 deflects electron beam 115 from the first side of screen 120 to the second side of screen 130 to draw a second line L2. This process continues very rapidly so that lines L3 through LN (where N=1, 2, 3, . . . , N) are drawn thereby creating a raster on screen 130.
To produce an accurate image, the distance dN (where n=1, 2, 3, . . . , N) between each horizontal line LN drawn on screen 130 must be equal as shown in FIG. 1B. The distance between each horizontal line dN is a function of two factors: the vertical angle of deflection xcex8 and the shape of screen 130. If the shape of the screen is spherical, a vertical deflection current signal IV having a sawtooth shaped waveform can be used. A sawtooth shaped waveform can be used since the distance from the point of deflection 129 to the upper, center, and lower portions of the curved screen is constant. If the shape of the screen is non-spherical (e.g., a flat screen), a vertical deflection current signal IV having a more complex S-shaped waveform must be used. An S-shaped waveform must be used since the distance from the point of deflection 129 to the upper and lower portions of a non-spherical screen is greater than the distance from the point of deflection 129 to the center portions of a non-spherical screen. Note that if the shape of the screen is non-spherical and a vertical deflection current signal IV having a sawtooth shaped waveform is used, the distance dN between horizontal lines LN drawn on screen 130 will not be an equal from one another as shown in FIG. 1C. This degrades the quality of the image drawn on screen 130 and thus is commercially undesirable.
As is well-known in the art, an S-shaped waveform can be produced by combining a sawtooth waveform with higher-order odd multiples of the sawtooth waveform. In particular, S-shaped waveforms be produced by combining the following components: a first-order signal component (i.e., a sawtooth signal), a third-order signal component, and a fifth-order signal component. Other higher-order odd signal components can also be combined with the sawtooth waveform to produce a more complex S-shaped waveform. FIG. 2 shows waveforms for a first-order signal component 210, a third-order signal component 220, and a fifth-order signal component 230, respectively.
FIG. 3 shows a conventional horizontal deflection generator circuit 300 that can be used to generate a vertical deflection current signal IV having an S-shaped waveform. Horizontal deflection generator circuit 300 includes a first-order signal generator 302, a first-order amplitude signal generator 304, a multiplier 306, a third-order signal generator 308, a third-order amplitude signal generator 310, a multiplier 312, a fifth-order signal generator 314, a fifth-order amplitude signal generator 316, a multiplier 318, and a signal combiner 320.
In operation, first-order signal generator 302 generates a first-order signal S1 and first-order amplitude signal generator 304 generates a first-order amplitude signal A1. Multiplier 306 multiplies first-order signal S1 with first-order amplitude signal A1 to generate a first-order vertical correction signal component A1S1. Third-order signal generator 308 generates a third-order signal S3 and third-order amplitude signal generator 310 generates a third-order amplitude signal A3. Multiplier 312 multiplies third-order signal S3 with third-order amplitude signal A3 to generate a third-order vertical correction signal component A3S3. Fifth-order signal generator 314 generates a fifth-order signal S5 and fifth-order amplitude signal generator 316 generates a fifth-order amplitude signal A5. Multiplier 318 multiplies fifth-order signal S5 with fifth-order amplitude signal A5 to generate a fifth-order vertical correction signal component A5S5.
Signal combiner 320 combines the vertical correction signal components A1S1, A3S3, and A5S5 to produce vertical correction signal AVSV. Vertical correction signal AVSV can be equivalent to vertical deflection current signal IV, or vertical correction signal AVSV can be further processed (e.g., amplified) prior to becoming vertical deflection current signal IV.
During the manufacturing process of a raster display system, a user must adjust amplitude signals A1, A3, and A5 so that lines L1 through line LN (where N=1, 2, 3, . . . , N) are properly drawn on screen 130. First, the user adjusts amplitude signal A1 so that line L1 is drawn at the proper position at the top of screen 130. This is referred to as setting the vertical size (i.e., the maximum angle of vertical deflection xcex8MAX). Next, the user adjusts amplitude signals A3 and A5 so that the distances dN between each horizontal line LN drawn on screen 130 are equal as shown in FIG. 1B. Unfortunately, when the user adjusts amplitude signals A3 and A5, the vertical size changes. As a result, the user must readjust amplitude signal A1 to reposition line L1 at the proper position at the top of screen 130. However, the readjustment of amplitude signal A1 causes the distances dN between each horizontal line LN drawn on screen 130 to become unequal again. Consequently, the user must readjust amplitude signals A3 and A5 so that the distances dN between each horizontal line LN drawn on screen 130 are equal. Unfortunately, the adjustment of amplitude signals A3 and A5 again causes the vertical size to change. As a result, the user must readjust amplitude signal A1 to reposition line L1 at the proper position at the top of screen 130. This time-consuming, inexact, trial-and-error process must be performed numerous times before amplitude signals A1, A3, and A5 are properly set.
Accordingly, what is needed is a circuit and method that allows the amplitudes of vertical correction signal components to be adjusted independently.
The present invention provides a technique that allows the amplitudes of vertical correction signal components to be adjusted independently. When the amplitude of each of the vertical correction signal components are set, they will not have to be readjusted when the amplitudes of the other vertical correction signal components are set. This greatly simplifies the process of setting the amplitudes of the vertical correction signal components, saving time and increasing the accuracy of the settings.
In one embodiment of the present invention, a circuit that allows the amplitudes of vertical correction signal components to be adjusted independently is provided. The circuit includes a first signal combiner having a first input coupled to
receive a first-order amplitude signal and a second input coupled to receive a third-order amplitude signal, a first multiplier having a first input coupled to receive a first-order signal and a second input coupled to receive an output signal of the first signal combiner, a second multiplier having a first input coupled to receive a third-order signal and a second input coupled to receive the third-order amplitude signal, and a second signal combiner having a first input coupled to receive an output signal of the first multiplier and a second input coupled to receive an output signal of the second multiplier.
In another embodiment of the present invention, a method that allows the amplitudes of vertical correction signal components to be adjusted independently is provided. The method includes combining a first-order amplitude signal with a third-order amplitude signal to generate a modified first-order amplitude signal, multiplying a first-order signal with the modified first-order amplitude signal to generate a first-order vertical correction signal component, multiplying a third-order signal with the third-order amplitude signal to generate a third-order vertical correction signal component, and combining the first-order vertical correction signal component with the third-order vertical correction signal component.
In another embodiment of the present invention, a method for generating a vertical deflection current signal including a first vertical correction signal component and a second vertical correction component is provided. The method includes setting an amplitude of the first vertical correction signal component, and setting an amplitude of the second vertical correction signal component, wherein the amplitude of the first vertical correction signal component will not have to be reset after the amplitude of the second vertical correction signal component has been set.
Other embodiments, aspects, and advantages of the present invention will become apparent from the following descriptions and the accompanying drawings.